The heat exchanger of the present invention is a condensation exchanger, designed to equip a gas or fuel boiler, in particular for industrial or domestic uses, for example in order to feed a central heating circuit and/or to provide water for sanitary use.
It is more specifically a triple exchanger, consisting of two main exchangers, each directly exposed to the hot gases generated by a gas or fuel burner, and a secondary exchanger, which is exposed to the gases, of a clearly lower temperature, that come from at least one of these main exchangers, or even both at the same time.
The water, or any other fluid to be heated, circulates entirely or partially in this secondary exchanger, where it is subjected to a preheating, then in a primary exchanger, where it is subjected to an actual heating.
As an example, the gases burned directly, coming from the burner, are at a temperature on the order of 1,000° C.
After having passed through a main exchanger, their temperature is generally between 100 and 180° C.
These hot gases contain a certain amount of water in the form of steam, which is capable of condensing when it comes into contact with the wall of the secondary exchanger, once it is below the dew-point temperature, on the order of 60° C.
This condensation has the effect of providing additional heat energy to the water circulating in the secondary exchanger, which additional heat energy corresponds to the latent heat of vaporization.
A double exchanger of this type, which is described for example in document EP 0 078 207, makes it possible to substantially improve the efficiency of the apparatus.
Document WO 94/16272 describes a heat exchanger element that consists of a tube made of a thermally conductive material, in which a heat-carrying fluid, for example the water to be heated, is intended to circulate.
This tube is wound in a spiral and has a generally oval planar cross-section, of which the large axis is substantially perpendicular to the axis of the spiral, and each coil of the tube has planar faces that are separated from the faces of the adjacent coil by a gap with a constant width, substantially lower than the thickness of said cross-section, with the spacing between two adjacent coils moreover being calibrated by means of spacers, which can consist, for example, of bosses formed in the wall of the tube.
This document also describes heat exchangers comprising a plurality of elements as above, which are arranged in different ways in the various embodiments mentioned.
An exchanger element thus designed allows for a very significant heat exchange between the hot gases that come into contact with the tubular element and the fluid to be heated that circulates inside it.
Indeed, when it passes through the gap between the coils, the flow of hot gases is in contact with a relatively extended surface of the wall of the exchanger element.
According to the embodiment shown in FIG. 22 of the aforementioned document WO 904/16272, to which reference can be made as necessary, the apparatus comprises two parallel bundles of tubes, a primary one 1 and a secondary one 1′.
These two bundles are arranged near one another, with their axes parallel, and are mounted securely inside a casing 8 (referred to as the “body” in the document).
The hot gases are supplied by an external apparatus 9 and penetrate, via a conduit 90 and a sleeve 80, the central portion of the main exchanger 1 (arrows J0). The hot gases pas through the latter radially, from the inside to the outside (arrows J1), then pass through the secondary exchanger, still radially, but this time from the outside to the inside (arrows J2).
Finally, the cooled gases leave this double exchanger through a sleeve 81 (arrows J3).
An improvement of this apparatus, intended in particular to improve the efficiency and compactness thereof, was the subject of WO 2004/016995, to which reference can also be made as necessary. It was derived from the observation made by the inventor that the energy to be recovered in the secondary exchanger is always lower than that captured by the primary exchanger.
Said improvement, which, according to the applicant, is the prior art closest to the present invention, relates to a condensation heat exchanger associated with a gas or fuel burner, which is composed of two bundles arranged near one another and mounted securely inside the a gas-tight casing, which two bundles communicate with one another by means of a so-called “transfer” collector, with means being provided in order to circulate a fluid to be heated, in particular cold water, first inside the tube(s) constituting said secondary bundle, then—via said transfer collector—inside the tube(s) constituting said primary bundle, wherein said casing surrounds the two bundles of tubes, while being slightly spaced apart from each of them, and said casing has a burned gas discharge sleeve positioned in the vicinity of said secondary bundle, which exchanger is thus arranged so that the hot gases generated by the burner pass radially, or approximately radially, by passing through the gaps separating their coils, first through said primary bundle, then said secondary bundle, and are then discharged from the exchanger through said sleeve.
It has essentially the following features:                the burner is housed coaxially inside the primary bundle;        the axial dimension of the secondary bundle is substantially smaller than that of the primary bundle, so as to provide an available space opposite an end portion of the primary bundle, in the extension of the secondary bundle of shorter length;        this available space is occupied by a chamber that communicates with the space inside the secondary bundle;        the sleeve is connected to the wall of the chamber so as to communicate with it, and is oriented transversely with respect to the axis of the secondary bundle, so that its bulk in the axial direction is contained in the chamber.        
An objective of the invention is to propose an exchanger of the type mentioned above, of which the power is substantially further improved, without notably changing its bulk.
Another objective of the present invention is to propose an exchanger with an increased range of powers that is capable of operating under optimal conditions of efficiency and safety at any point in said range; by way of indication, this range may be from 25 to 500 kW, for example.